Doctors are testing a smart electronic scalpel dubbed the "iKnife" that knows when it is cutting cancer cells.Shutterstock

An “intelligent” knife that knows when it is cutting through cancerous tissue is being tested in three London hospitals.

Experts believe the wand-like device, the first of its kind in the world, will revolutionize cancer treatment by removing uncertainty from surgery.

The device – called the iKnife – is a hi-tech form of “electric scalpel”, a tool routinely used by surgeons that uses electricity to sear through membranes and internal organs.

But, in addition, the knife is able to indicate exactly where the cancerous tissue is, and when it has all been removed.

As the iknife cuts, smoke from the burned tissue is pumped through a tube into a mass spectrometer, a machine that uses magnetism to produce a chemical “fingerprint” of the atoms fed into it and an operating surgeon can learn almost instantly if a suspicious growth is cancerous or benign.